Chemical analysis cuvette

ABSTRACT

Improved components, such as a cuvette, are disclosed in the specification.

RELATED APPLICATION

This application is a Division of my application Ser. No. 133,081 filedApr. 12, 1971, now U.S. Pat. No. 3,748,044, entitled "Digital ChemicalAnalysis Apparatus".

BACKGROUND OF THE INVENTION

This invention relates to a chemical analysis cuvette, and moreparticularly relates to a cuvette which enables the analysis ofsubstances by radiant energy.

In order to rapidly analyze the concentration of a particular substancepresent in a chemical specimen, such as blood, chemists are placingincreasing reliance on various types of machines. Such machines devisedin the past may be divided into at least the following types:

1. Blood gas analyzers;

2. Prothrombin time determining systems;

3. Flow systems;

4. Electromechanical methods not related to colorimetry; and

5. Monochromatic servomechanism systems.

Although such machines have somewhat reduced the labor involved inperforming chemical analysis, they have exhibited many deficiencies thathave limited their overall usefulness. One such deficiency is thedifficulty of loading and cleaning the specimen dispensers and cuvettesof prior art systems. Such difficulties are particularly pronounced whenflow-through cuvettes are utilized. These cuvettes provide a singlechamber for analyzing multiple specimens that must be purged with arelatively large volume of specimen fluid each time a new specimen isintroduced into the chamber. Prior art systems also fail to mix thespecimen and reagent with the degree of accuracy desired by mostchemists.

In order to overcome the difficulties of the prior art devices,applicant's cuvette means preferably comprises integrally-formedsidewalls and spacer means that define compartments in which specimensmay be introduced. Opposed, planar window means for transmitting radiantenergy may also be provided in the compartments so that the specimensmay be analyzed with a degree of accuracy unattained by systemsemploying curved windows, such as test tubes. By integrally fabricatingthe sidewall and spacer means from the plastic material describedherein, the cuvette means is rendered disposable, thereby eliminatingthe most common cause of specimen contamination.

DESCRIPTION OF THE DRAWINGS

These and other advantages and features of the present invention willhereinafter appear for purposes of illustration, but not of limitation,in connection with the accompanying drawings, in which like numbersrefer to like parts throughout, and in which:

FIG. 1 is a perspective view of a preferred form of apparatus made inaccordance with the present invention;

FIG. 2 is a top plan view of a preferred form of cuvette assembly madein accordance with the present invention;

FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 2;

FIG. 4 is a side elevational view of the cuvette assembly shown in FIG.2;

FIG. 5 is a cross-sectional, fragmentary, partially schematic viewshowing the cuvette assembly, carrousel assembly, cycling apparatus,positioning apparatus, and a portion of the analyzing apparatus of thepreferred embodiment;

FIG. 6 is a front elevational view of a preferred form of positionencoding apparatus made in accordance with the present invention; and

FIG. 7 is a fragmentary, partially cross-sectional side elevational viewof a preferred form of carrousel advance apparatus made in accordancewith the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, a preferred system for analyzing chemicalspecimens made in accordance with the present invention basicallycomprises a cuvette assembly 30; a carrousel assembly 110, including acycling assembly 168; a dispenser assembly 200; and a console 502 thatincludes analyzing apparatus, a processing circuit and a memory.

Referring to FIGS. 1-4, cuvette assembly 30 provides 32 compartments inwhich 32 separate chemical specimens may be mixed and held for analysis.The assembly is integrally formed from an acrylic plastic material thattransmits ultraviolet light, such as Rohm and Haas PlexiglasV(811)-100UVT. Applicant has found that this material offers a number ofadvantages. It is relatively inexpensive, and therefore enables thecuvette to be disposed of after use. In addition, the described acrylicplastic offers excellent optical properties for the transmission ofultraviolet light which are not provided by many other acrylic plastics.

Referring to FIGS. 2-4, cuvette assembly 30 comprises a slanting, innersidewall 32 having an inner surface 34 and an outer surface 36. Cuvetteassembly 30 also comprises a slanting, outer sidewall 40 having an innersurface 42 and an outer surface 44. Sidewalls 32 and 40 are each slantedat an angle of 15° from a vertical plane. Applicant has found that thisis the minimum angle required to prevent specimen fluid from splashingout of the cuvette as it is being discharged therein.

Another portion of cuvette assembly 30 comprises a cylindrical collar 50having an upper edge 52, a lower edge 54, and a central axis 56. Collar50 defines a ventilating opening 55 that allows the passage of air.

Assembly 30 further comprises a positioning lip 92 attached to outersidewall 40 in the manner shown. Lip 92 has notches, such as notches 94,96 that are equally spaced between each other and are located along acenter line radius of a compartment.

Spacers 58 are integrally formed with the sidewalls in a fluid-tightmanner to form 32 separate compartments 60-91. The compartments liealong a line defining a circle. The lower portion of each spacer issplit into two sections 57,59 that separate each of the compartments byan air space 53. This feature enables several cuvettes to nest on top ofeach other, thereby reducing the space required for storage. Inaddition, this air space allows the fluid of an incubating device toseparately flow around each compartment, thereby reducing the timerequired to bring the specimens up to temperature. This feature will bedescribed in more detail later. Each of the compartments is adapted tohold a specimen to be analyzed. The lower portion of each compartment isfitted with a bottomwall that is integrally formed with the adjacentspacers and sidewalls in a fluid-tight manner. Exemplary bottomwalls 48have curved upper surfaces 49 that cause fluid ejected into thecompartments to engage in a swirling motion that aids mixing.

Each of the compartments 60-91 is identical and may be understood fromexemplary compartments 67 and 83 shown in FIG. 3. Compartment .[.67.]..Iadd.83 .Iaddend.comprises the sidewalls and bottomwalls describedpreviously. In addition, compartment .[.67.]. .Iadd.83.Iaddend.comprises flat, planar portions 98 and 100 that form a windowsection 38. Likewise, compartment .[.83.]. .Iadd.67 .Iaddend.comprisesthe sidewall and bottomwall described previously. In addition, itcomprises flat, planar portions 102 and 104 that form a window section46. It should be noted that portions 98, 100 are opposed planar membersthat are parallel to each other. Likewise, portions 102, 104 are alsoopposed planar members that are parallel to each other and to portions98, 100. As can be seen in FIGS. 2-4, the flat planar portions formingthe window sections lie in a common plane and are integrally formed withthe bottomwall and sidewalls. It should be noted that sidewalls 32 and40 are each 0.040 inches thick, and that the distance between planarportions 98, 100 and the distance between planar portions 102, 104 is ineach case exactly 1 centimeter.

As will be described in more detail later, this arrangement of windowsections provides an accurate path-length for a radiant energy analyzingbeam not found in the test tube cuvettes employed in some systems.Moreover, since the entire cuvette assembly is made from a relativelyinexpensive plastic, it may be disposed of after a single use so as toprevent contamination from previous or improper washing. Thedisposability of the cuvette is very important, since it eliminates thenecessity of using large volumes of reagent to wash the previous samplefrom a flow-through cuvette. By using the cuvette assembly describedherein, the same compartment is used as a reaction chamber and radiantenergy analyzing chamber, thereby achieving economy of operation and amore compact system than would be otherwise possible.

Referring to FIGS. 1 and 5, carrousel assembly 110 comprises acylindrical base member 112 that supports platforms 114, 115. Platform114 carries cylindrical support column 116 through which air iscirculated by a fan 118 for cooling purposes. A cylindrical outer column120 is carried by the top of column 116.

An incubator assembly 122 comprises a generally toroidal bath chamber124 which is formed by a hollow receptacle 125 comprising a cylindricalinner wall 126 and a cylindrical outer wall 128. Wall 126 is integrallyformed with column 120. Walls 126 and 128 are fabricated from a goodthermal conducting material such as aluminum or copper. Windows thatreadily pass radiant energy in order to accommodate analyzing apparatusdescribed hereafter are located in walls 126 and 128. Bath chamber 124is filled with water to level A shown in FIG. 5. The water is heated topredetermined temperature by a heater element 129, and the heaterelement is controlled by a thermistor 131 and a manually adjustablecontrol switch (not shown). As shown in FIG. 5, the incubator is used inorder to maintain the specimens held in the cuvette compartments at apredetermined temperature. As previously described, the cuvettecompartments are separated so that the water of incubator assembly 122freely flows adjacent each specimen. Applicant has found that thisarrangement brings the specimens up to temperature faster and holds thespecimens at a more uniform temperature than has heretofore beenpossible.

Still referring to FIGS. 1 and 5, assembly 110 is provided with amovable positioning platform 130 comprising a cylindrical skirt 132 anda ring-shaped test tube retainer 134. The retainer comprises ahorizontal ring member 136 that is provided with holes for receiving 32test tubes commonly designated by the number 138, and includingexemplary test tubes 140, 141. Each of the test tubes lies along aradius common to a corresponding cuvette compartment. The retainer alsocomprises a vertical ring-shaped retainer 142. According to thepreferred embodiment of the invention, the test tubes are used to holdchemical samples prior to the time they are mixed with a suitablereagent to form a specimen for analysis. The tubes are biased againstretainer 142 by resilient spring clips, such as exemplary clips 143,144. The clips are mounted on skirt 132.

Positioning platform 130 also comprises a raised, ring-shaped portion146 that carries on its underside a circular positioning member 148bearing detents. Member 148 is provided with one detent opposite eachtest tube and corresponding cuvette compartment, so that each specimenmay be accurately located in a predetermined analyzing position duringthe analysis procedure. The entire positioning platform is rotatablymounted on the platform 115 by means not shown. The inner edges ofplatform 130 are fitted with guides, such as guides 149, 150 that comatewith the notches of lip 92 of cuvette assembly 30. By using the guides,the cuvette assembly is precisely located on the platform and isrotatable therewith.

Cylindrical skirt 132 comprises 32 sets of five coded holes that aredrilled adjacent a radial line extending from each cuvette compartment.An exemplary set of 152 of such coded holes are shown in FIG. 6.Referring again to FIG. 5, light is transmitted through the coded holesto a plurality of stationary phototransistors 154 by a light pipe 156.As explained in more detail later, the coded holes are used to generatea binary identity code that uniquely identifies each test tube andcorresponding cuvette compartment that is moved into the analyzingposition. That is, each of the test tubes and corresponding cuvettecompartments is identified by a different arrangement of coded holeswhich can be recognized and used to perform certain machine functions.The manner in which cells 54 are arranged in order to recognize the holebinary code is well-known to those skilled in the art.

As shown in FIG. 5, a test tube detection assembly 158 is held in acabinet 160 that is located one position ahead of the analyzingposition. The assembly comprises a pendulum 162 pivoted around a rod164. The pendulum normally swings into the path of test tubes 138, andin that position, causes a mercury switch 166 to be closed. When a testtube is positioned opposite assembly 158, pendulum 162 is moved to theposition shown in FIG. 5, thereby causing switch 166 to open. Assembly158 is arranged so that the normal operation of the system isinterrupted if no test tube is present at a particular position in ringmember 136.

Carrousel assembly 200 also comprises a cycling assembly 168 shown inFIG. 7. Assembly 168 comrises a solenoid 170 that operates an actuatorarm 172 comprising an upper arm 171 and a lower arm 173 that pivot abouta bearing 174. Assembly 168 also comprises a metallic bellows 176 thatis normally filled with oil. A flexible hat-section 177 is located abovethe bellows and is connected thereto by a flapper valve 178 thatcontrols the movement of oil. A spring 180 mounted on actuator arm 172biases a roller arm 182 in an upward direction (as shown in FIG. 7). Aroller 184 is rotatably mounted at the outer end of roller arm 182 andis biased into contact with the detents of positioning member 148, suchas exemplary detents 185, 186. As previously described, positioningmember 148 is rigidly attached to positioning platform 130 on whichcuvette 30 is carried. The biasing action of spring 180 ensures theprecise positioning of the positioning platform at all times.

The cycling assembly operates as follows. When solenoid 170 isactivated, it forces upper arm 171 to the right (as shown in FIG. 7),and forces lower arm 173 upward, thereby compressing bellows 176 in anupward direction. This force is resisted by the bellows which is filledwith oil. In order to relieve the oil pressure, flapper valve 178 opens,thereby permitting oil from the bellows to flow freely into flexiblehat-section 177. As upper arm 171 is moved to the right, roller 184 isremoved from detent 185 and is repositioned in detent 186. The foregoingmotion of the actuator arm is extremely rapid, so that the carrouselpositioning platform 130 temporarily remains in a stationary position.At the completion of the solenoid stroke, the actuator arm reaches theposition shown in phantom in FIG. 7. At this time, the solenoid isde-energized, and the resiliency of the metallic bellows biases theactuator arm toward its original position. The return of the actuatorarm to its original position is damped by the closing of flapper valve178. The flapper valve is provided with a hole therein so that the oilcan leak into the metallic bellows at a predetermined rate, therebyproviding a smooth, steady return motion to the actuator arm. As aresult, when the actuator arm is returned to its initial position,detent 186 is moved to the position formerly occupied by detent 185, sothat positioning platform 130 is advanced one position. As thepositioning platform is advanced, the cuvette compartments are alsoadvanced one position.

A stop lever 188 having a threaded adjustment screw 189 is used toadjust the normal position of the actuator arm so that the positioningplatform will support the cuvette assembly in an exact, predeterminedposition after every solenoid stroke. The cycling assembly is used tosequentially advance the cuvette compartments into the path of ananalyzing beam.

Referring to FIG. 5, light is passed through the cuvette by analyzingapparatus comprising a light source 402 having a filament 404 thatproduces light throughout the visible and ultraviolet spectrum. Thelight source is held in a socket 401 by a spring 403 and an indexingplate 405. The light source supplies light to lenses 406, 407 that focusthe light through a mirror 408 onto a ring-shaped filter 412 located ona disc 410, and to a commutator ring of disc 410. Disc 410 rotates aboutan axis located in the center thereof.

Disc 410 is rotated by a motor-gear unit 444 (FIG. 5) that rotates ashaft 446 through a magnetic coupling 448 and bearings 450, 452. Unit444 is geared to rotate disc 410 at about 1800 rmp.

When filter 412 is being rotated, light from source 402 passestherethrough and generates beams of light along a single path 454. Themonochromatic light pulses generated by the filter and source 402 in asingle path pass through each specimen to be analyzed. For example, ifcompartment 83 of cuvette 30 is located in the analyzing position shownin FIG. 5, the pulses are passed through a lens 456, reflected from amirror 457, and transmitted through the incubator bath chamber 124. Thepulses thereafter pass through planar portion 98 of cuvette 30, thespecimen in compartment 83, planar portion 100, bath chamber 124, amirror 458, and another lens 460 that focuses the resulting transmittedpulses onto a portion of filter 412 that is 180° displaced from theportion of the filter which produced the pulses. Since correspondingidentical segments of the filter are displaced by 180° of arc, eachpulse is filtered by identical filters before it enters the specimen andafter it leaves the specimen.

After the pulses transmitted from the specimen pass through filter 412,they are transmitted into a photomultiplier transducer tube 462 thatsequentially produces electrical pulse signals having valuesproportional to the intensity of the light transmitted through thespecimen. Preferred apparatus for processing signals produced by tube462 is shown in the above-described related application which isincorporated by reference.

Those skilled in the art will appreciate that the specific embodimentsdescribed herein may be altered and changed by those skilled in the artwithout departing from the true spirit and scope of the invention whichis defined in the appended claims.

What is claimed is:
 1. In a chemical analyzer, an improved cuvettecomprising:integrally formed means for defining individual compartmentsadapted to hold specimens, said compartments being arranged to passthrough a line defining a closed curve having a central axis; .[.and.].window means .Iadd.associated with each compartment comprising opposedplanar members that are parallel to each other .Iaddend.for transmittingradiant energy through at least some portions of the compartments,whereby the specimens may be analyzed.Iadd.; ventilation means fordefining an opening within said curve for allowing the passage of air;and additional analyzing apparatus comprising: a source of radiantenergy located within the area bounded by a vertical projection of saidline defining a closed curve;rotation means for rotating the cuvette inrelationship to the radiant energy source, whereby the radiant energysequentially passes through the window means in each of saidcompartments; and means for passing air over the source and through saidopening, whereby the source is cooled. .[.
 2. A cuvette, as claimed inclaim 1, and further comprising ventilation means for defining theopening within said curve for allowing the passage of air..]. .[.3. Acuvette, as claimed in claim 1, wherein a common plane intersects eachof the window means..]. .[.4. A cuvette, as claimed in claim 1, whereinthe window means associated with each compartment comprises opposedplanar members that are parallel to each other..]. .[.5. A cuvette, asclaimed in claim 1, wherein the compartments comprise sidewall means andwherein the window means are formed integrally with the sidewallmeans..]. .[.6. A cuvette, as claimed in claim 1, wherein eachcompartment comprises bottomwall means that are curved adjacent thecompartment..].
 7. A cuvette, as claimed in claim .[.1.]..Iadd.14.Iaddend., wherein the window means are fabricated from materialthat transmits ultraviolet light.
 8. A cuvette, as claimed in claim 7,wherein the window means are fabricated from acrylic. .[.9. A cuvette,as claimed in claim 1, wherein the compartments are interrupted by airspaces..]. .[.10. A cuvette, as claimed in claim 9, and furthercomprising temperature control means for maintaining the specimens at apredetermined temperature comprising:a bath solution in which thesidewall means are at least partially immersed so that the bath solutionenters the air spaces between the compartments; and means formaintaining the bath solution at a constant temperature..]. .[. Acuvette, as claimed in claim 2, in combination with additional analyzingapparatus comprising a source of radiant energy located within the areabounded by a vertical projection of said line defining a closedcurve..]. .[.12. Apparatus, as claimed in claim 11, and furthercomprising:rotation means for rotating the cuvette in relationship tothe radiant energy source, whereby the radiant energy sequentiallypasses through the window means in each of said compartments; and meansfor passing air over the source and through said opening, whereby thesource is cooled..].
 13. Apparatus, as claimed in claim .[.12.]..Iadd.1.Iaddend., wherein the source is aligned so that the radiantenergy is transmitted perpendicular to the surface of the window meansat some time during the operation of the rotation means. .Iadd.14. Animproved cuvette for use in a chemical analyzer comprising:integrallyformed means for defining individual compartments adapted to holdspecimens, said compartments having an open end and a closed end andbeing arranged to pass through a line defining a closed curve having acentral axis, said integrally formed means comprisingan outer sidewalldefining an outer edge which fits within a circle having a center pointlying in the central axis and defining a first slanting surface which isa common boundary for the compartments and which is slanting withrespect to the central axis, an inner sidewall defining a secondslanting surface which is a common boundary for the compartments andwhich is slanting toward the first slanting surface, bottomwall meansextending between the outer and inner sidewalls adjacent the closed endof the compartments, a plurality of spacer means integrally formed withthe outer sidewall, inner sidewall and bottomwall means for preventingthe transfer of a specimen between adjacent compartments, each saidspacer means comprisingan upper section at least partially locatedadjacent the open end of a compartment, a first lower section integrallyformed with a first one of the plurality of bottomwall means and asecond lower section integrally formed with a second one of theplurality of bottomwall means, the first and second lower sections beingseparated by an air space, whereby heated fluid can flow around eachcompartment to incubate the specimens; lip means integrally formed withthe outer sidewall and extending radially outward from the outer edge ofthe outer sidewall for supporting and securing the cuvette; ventilationmeans for defining an opening within the inner sidewall for allowing thepassage of air; and window means for transmitting radiant energy throughat least some portions of each of the compartments comprising an opposedpair of planar members separated by a predetermined distance located ineach compartment, one of the planar members in each pair beingintegrally formed with the outer sidewall and the other of the planarmembers in each pair being integrally formed with the inner sidewall,each of said planar members intersecting a common plane, whereby thespecimens may be analyzed. .Iaddend. .Iadd.15. A cuvette, as claimed inclaim 14, wherein the first slanting surface defines a portion of thelateral area of a first cone and wherein the second slanting surfacedefines a portion of the lateral area of a second cone which intersectsthe first cone. .Iaddend. .Iadd.16. A cuvette, as claimed in claim 15,wherein any line lying in the lateral area of the first cone andintersecting the central axis makes a predetermined acute angle withrespect to the central axis and wherein any line lying in the lateralarea of the second cone and intersecting the central axis also makessubstantially the same predetermined acute angle with respect to thecentral axis. .Iaddend. .Iadd.17. A cuvette, as claimed in claim 16,wherein the predetermined acute angle is at least 15 degrees, so thatthe specimen is inhibited from splashing as the compartment is beingfilled. .Iaddend. .Iadd.18. A cuvette, as claimed in claim 14, whereinthe outer sidewall comprises a first upper edge adjacent the open end ofthe compartments defining a first circle having a first center pointlying in the central axis, and wherein the inner sidewall comprises asecond upper edge adjacent the open end of the compartments defining asecond circle having a second center point lying in the central axis..Iaddend. .Iadd. A cuvette, as claimed in claim 18, wherein the innerand outer sidewalls are each 0.04 inch thick. .Iaddend. .Iadd.20. Acuvette, as claimed in claim 14, wherein the lip means comprises aplanar upper surface defining a first plane perpendicular to the centralaxis and a planar lower surface defining a second plane parallel to thefirst plane. .Iaddend. .Iadd.21. A cuvette, as claimed in claim 20,wherein the lip means defines an outer perimeter and comprises aplurality of positioning notches, each said positioning notch beinglocated adjacent the perimeter and opposite one of the compartments..Iaddend. .Iadd.22. A cuvette, as claimed in claim 21, wherein eachpositioning notch and the compartment located opposite the positioningnotch are bisected by a plane passing through the central axis..Iaddend. .Iadd.23. A cuvette, as claimed in claim 22, wherein eachpositioning notch includes an arcuate shaped section. .Iaddend..Iadd.24. A cuvette, as claimed in claim 23, wherein a positioning notchis located opposite each compartment. .Iaddend. .Iadd.25. A cuvette, asclaimed in claim 14, wherein the predetermined distance between theplanar members is one centimeter, and wherein the planar members in eachpair are substantially parallel. .Iaddend. .Iadd. A cuvette as claimedin claim 25, wherein the upper section of each spacer means is planarand wherein the air space is wider than the planar upper section, sothat the cuvette can be nested with another like cuvette. .Iaddend..Iadd.27. A cuvette, as claimed in claim 26, wherein each planar uppersection of each spacer means is bisected by a plane which passes throughthe central axis. .Iaddend. .Iadd.28. A cuvette, as claimed in claim 14,wherein each bottomwall means is curved adjacent a compartment so thatmixing of the specimen is aided. .Iaddend. .Iadd.29. A cuvette, asclaimed in claim 14, wherein the ventilation means comprises a hollowcollar integrally formed with the inner sidewall, whereby air may passthrough the hollow portion of the collar. .Iaddend. .Iadd.30. A cuvette,as claimed in claim 29, wherein the collar defines a cylinder having anaxis colinear with the central axis and defines a circular upper edgelying in a plane perpendicular to the central axis. .Iaddend. .Iadd.31.A cuvette, as claimed in claim 15, wherein the lip means defines anouter perimeter and comprises a plurality of positioning notches, eachsaid positioning notch being located adjacent the perimeter and oppositeone of the compartments. .Iaddend. .Iadd.32. A cuvette, as claimed inclaim 31, wherein each bottomwall means is curved adjacent a compartmentso that mixing of the specimen is aided. .Iaddend. .Iadd.33. A cuvette,as claimed in claim 32, wherein the ventilation means comprises a hollowcollar integrally formed with the inner sidewall, whereby air may passthrough the hollow portion of the collar. .Iaddend. .Iadd.34. A cuvette,as claimed in claim 33, wherein any line lying in the lateral area ofthe first cone and intersecting the central axis makes a predeterminedacute angle with respect to the central axis and wherein any line lyingin the lateral area of the second cone and intersecting the central axisalso makes substantially the same predetermined acute angle with respectto the central axis. .Iaddend. .Iadd.35. A cuvette, as claimed in claim34, wherein each positioning notch and the compartment located oppositethe positioning notch are bisected by a plane passing through thecentral axis. .Iaddend. .Iadd.36. A cuvette, as claimed in claim 35,wherein the upper section of each spacer means is planar and wherein theair space is wider than the planar upper section, so that the cuvettecan be nested with another like cuvette. .Iaddend. .Iadd.37. A cuvette,as claimed in claim 36, wherein the collar defines a cylinder having anaxis colinear with the central axis and defines a circular upper edgelying in a plane perpendicular to the central axis. .Iaddend. .Iadd.38.A cuvette, as claimed in claim 37, wherein the predetermined acute angleis at least 15 degrees, so that the specimen is inhibited from splashingas the compartment is being filled. .Iaddend. .Iadd.39. A cuvette, asclaimed in claim 38, wherein a positioning notch is located oppositeeach compartment, and wherein each positioning notch includes an arcuateshaped section. .Iaddend. .Iadd.40. A cuvette, as claimed in claim 39,wherein each planar upper section of each spacer means is bisected by aplane which passes through the central axis. .Iaddend. .Iadd.41. Acuvette, as claimed in claim 40, wherein said plane which passes throughthe central axis also bisects said air space. .Iaddend. .Iadd.42. Acuvette, as claimed in claim 41, wherein the inner and outer sidewallsare 0.04 inch thick, wherein the predetermined distance between theplanar members is one centimeter, and wherein the planar members in eachopposed pair are substantially parallel. .Iaddend.